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Supercapacitor charger has auto cell balancing

Posted: 19 Jun 2008     Print Version  Bookmark and Share

Keywords:supercapacitor charger  charge-pump  charge current  low-noise 

Linear Technology Corporation introduces the LTC3225, an inductorless programmable supercapacitor charger producing high peak power and serves battery backup needs in portable applications.

150mA Supercap charger with auto cell balancing

The device employs a low-noise charge-pump architecture to charge two supercapacitors in series to a fixed output voltage (4.8V/5.3V selectable) from a 2.8V to 5.5V input supply. Charge current is resistor programmable up to 150mA, and the device's automatic cell balancing feature maintains equal voltages on both cells (2.4V/2.65V selectable) without requiring balancing resistors. This protects each supercapacitor from over-voltage damage caused by mismatches in cell capacitance or leakage while minimising current drain on the capacitors. The LTC3225 will not discharge the supercapacitors when the input supply is removed or shorted to ground.

The LTC3225 operates with a very low 20uA quiescent current when the output voltage is in regulation and draws only 2uA from VOUT. Current is further reduced when the input supply is removed as the IC automatically enters a low current shutdown state, drawing less than 1uA from the supercapacitors. The basic charging circuit requires only 3 external components and takes up little space; the IC is offered in a tiny 6mm2 footprint DFN package. It is ideal for current-limited applications with high peak power loads such as LED flash PCMCIA Tx bursts, HDD bursts, and GPRS/GSM transmissions; in addition it may be used as a backup supply. Also, bigger board-level systems such as servers and RAID/mass storage systems often have a need for brief high-power backup supplies for which supercapacitors are well-suited. Other key features include automatic recharge, built-in current and thermal limiting, and high 1MHz operating frequency to reduce the size of external components.

The LTC3225 is housed in a compact 10-lead, low-profile (0.75mm) 2mm x 3mm DFN package, and operation from -40°C to 85°C ambient temperature is guaranteed. Pricing starts at Rs.80.04 ($2.00) each in 1,000-piece quantities.

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